Boiler Flue Gas and Oven Exhaust Economizer Systems

ABSTRACT

A representative mechanical draft system includes an in-line draft inducer that comprises a motor and a backward-inclined impeller. The mechanical draft system also includes an economizer coupled to the in-line draft inducer, where the economizer comprises a housing and a horizontally mounted heat recovery unit.

BACKGROUND

There are many types of boilers, ovens, and other heat generating appliances on the market that vent or exhaust differently. An atmospheric boiler with a draft hood or draft diverter relies on the natural draft, which typically range from 0.0 to 0.03 inch water column (inWC) draft. Even a small restriction in the chimney flue can cause the boiler to fail or prevent proper discharge of products of combustion.

A forced draft boiler used for steam or hot water has a built-in fan to push products of combustion through the venting system and the forced draft typically range from 0.0 to 0.5 inWC. Other boiler types fall in between these two extremes. As a result, it is generally a challenge to use flue gas economizers and they are rarely used with atmospheric boilers. Economizers used with forced draft boilers must generally be designed so that the resistance never exceeds 0.3-0.4 inWC, thereby causing such economizers to be voluminous and space consuming. This restriction also limits the number of boilers a single economizer can serve. Thus, in most applications, a dedicated economizer is needed for each boiler even when exhausted through a single common chimney.

Baking ovens and process ovens experience the same challenges as boilers. Often, there is no driving force in the exhaust stream, so it is very difficult to integrate a heat recovery unit in the exhaust stream to recapture the heat in the exhaust gases. In addition to the applications described above, other processing equipment such as cooling systems, smokehouses, drying equipment, brewing equipment, pasteurizers, etc. generate hot exhaust. Most of these applications face serious challenges when heat recovery is attempted, where such attempts often lead to oven failures, unintended processing results, and so on. There is therefore a need in the industry for devices capable of saving and recovering energy.

SUMMARY

Various embodiments of a mechanical draft system are disclosed. Briefly described, one embodiment of a mechanical draft system includes an in-line draft inducer that comprises a motor and a backward-inclined impeller. The mechanical draft system also includes an economizer coupled to the in-line draft inducer, where the economizer comprises a housing and a horizontally mounted heat recovery unit.

Another embodiment of a mechanical draft system includes an in-line draft inducer comprising a motor and a backward-inclined impeller. The mechanical draft system also includes an economizer detachably coupled to the in-line draft inducer, the economizer comprising a cylindrical housing for horizontally mounting a heat recovery unit that partitions the housing into an upper chamber and a lower chamber.

Another embodiment is a method implemented in a draft controller in a mechanical draft system comprising an in-line draft inducer and an economizer, the economizer comprising a heat recovery unit and a damper assembly. In response to a heat recovery request, a fan speed of the in-line draft inducer is increased based on a predetermined draft set point value. Upon reaching the draft set point value, a valve of the economizer is opened to allow fluid to flow through the heat recovery unit. The damper assembly is placed in a closed position to channel exhaust flow through the heat recovery unit, and in response to the damper assembly being placed in a closed position, the fan speed of the in-line draft inducer is increased to maintain the predetermined draft set point value.

Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 illustrates a mechanical draft system that comprises an economizer coupled to an in-line draft inducer according to various embodiments of the present disclosure.

FIG. 2A illustrates a first exhaust flow configuration where a turbulent exhaust flow is created such that flue gases flow through the lower chamber, through the heat recovery unit, and then into the upper chamber according to various embodiments of the present disclosure.

FIG. 2B illustrates a second exhaust flow configuration where the flue gases flow over and bypass the heat recovery unit according to various embodiments of the present disclosure.

FIG. 3 is an exploded view of the in-line draft inducer of FIG. 1.

FIG. 4A illustrates how the heat recovery unit is mounted on a guide rail assembly within the economizer, where the guide rail assembly is horizontally installed along a centerline of the economizer.

FIG. 4B illustrates the heat recovery unit inserted into the housing of the economizer and where the blades of the bypass damper assembly are in a closed position to block the flow of flue gases through the lower chamber of the economizer.

FIG. 5 illustrates NPT water connectors on a distal end of the heat recovery unit.

FIG. 6 is a side view of the economizer of FIG. 1, where the bypass damper assembly includes a series of lever arms that are pivotally connected to the blades of the bypass damper assembly.

FIG. 7 shows another embodiment of the bypass damper assembly in the economizer, where the bypass damper assembly comprises a single round damper blade.

FIG. 8 is a top view of the economizer and further illustrates how the heat recovery unit is slidably inserted into the economizer.

FIG. 9 is a side view of the economizer and further illustrates how the heat recovery unit partitions the housing of the economizer into an upper chamber and a lower chamber.

FIG. 10 is a flowchart illustrating an algorithm for controlling the various components of the mechanical draft system of FIG. 1 for facilitating the flow of flue gases according to various embodiments of the present disclosure.

FIG. 11A illustrates how the economizer and the in-line draft inducer are coupled together via a mating bolt flange and where the mechanical draft system is attached to a chimney in a substantially horizontal orientation according to various embodiments of the present disclosure.

FIG. 11B illustrates how the economizer and the in-line draft inducer are coupled together via mating bolt flanges and where the mechanical draft system is attached to a chimney in a substantially vertical orientation according to various embodiments of the present disclosure.

FIG. 12 illustrates another configuration wherein the economizer and the in-line draft inducer are separated from each other in the chimney system according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments of a mechanical draft system are disclosed that comprise an economizer that may be either fan-powered with an integrated draft fan or configured as a stand-alone unit. Reference is made to FIG. 1, which depicts a mechanical draft system 102 that comprises an economizer 104 coupled to an in-line draft inducer 110 according to various embodiments of the present disclosure. The modulating fan-powered economizer 104 shown can be used in various systems that include at least one appliance, such as, for example, a boiler, oven, water heater, fireplace, and so on.

In the embodiment of FIG. 1, the economizer 104 includes an inlet 101, an outlet 103 and a housing 105 positioned between the inlet 101 and outlet 103. The inlet 101 and the outlet 103 facilitate the flow of flue gases entering the economizer 104. The housing 105 may be constructed according to a round tube-type design where the flow path through the housing 105 is linear. The economizer 104 is equipped with a heat recovery unit 106 comprising a radiator style heat recovery unit constructed with copper tubing and fins. For other embodiments, the radiator style heat recovery unit may be constructed with 316 stainless tubing and fins.

As shown, the heat recovery unit 106 is horizontally mounted such that the main body portion of the heat recovery unit 106 is perpendicular to the flue gas flow. The economizer 104 is further equipped with a bypass damper assembly 108, where the bypass damper assembly 108 may comprise a butterfly damper or a multi-blade damper, as shown in FIG. 1. The bypass damper assembly 108 is controlled by a variable position actuator in the economizer 104, where the actuator configures the bypass damper assembly 108 to direct the exhaust flow in one of two exhaust flow configurations. In a first exhaust flow configuration, the flue gases flow pass over and through the heat recovery unit 106. Specifically, a turbulent exhaust flow is created such that flue gases flow through the lower chamber, through the heat recovery unit 106, and into the upper chamber, as shown in FIG. 2A.

In a second exhaust flow configuration, the flue gases flow over and bypass the heat recovery unit 106, as shown in FIG. 2B. This configuration prevents over-heating of the coils in case the liquid inside the coils is not flowing or if the exhaust heat exceeds the performance of the heat recovery unit 106. The combination of the variable position actuator and the bypass damper assembly 108 allow modulation of the exhaust air flow over the heat recovery unit 106 so that a variable percentage of the exhaust air can pass through the heat recovery unit 106 and the remainder bypass the heat recovery unit 106.

Referring back to FIG. 1, a tapered inlet member 112 may be coupled to the economizer 104 to further facilitate the channeling of exhaust flow. The diameter of the tapered inlet member 112 is constructed to allow the mechanical draft system 102 to be inserted into any type of commercial chimney. As shown, the tapered inlet member 112, the economizer 104, and the in-line draft inducer 110 may each include bolt flanges 113, 114, 115 for coupling the tapered inlet member 112, the economizer 104, and the in-line draft inducer 110 to each other.

Reference is made to FIG. 3, which is an exploded view of the in-line draft inducer 110 of FIG. 1. The in-line draft inducer 110 may be installed in-line in the vertical or horizontal section of a chimney or stack. In accordance with various embodiments, the in-line draft inducer 110 includes a backward inclined centrifugal impeller 112. The housing 119 of the in-line draft inducer 110 is constructed of stainless steel and is equipped with an enclosed variable speed motor. The centrifugal impeller 112 is an in-line fan where the inlet and outlet are on the same centerline. With the integration of a centrifugal impeller 112, the in-line draft inducer 110 can handle a great deal of pressure resistance, which is utilized in most applications to down-size ductwork. However, the centrifugal may also be used to reduce the perceived resistance in the economizer 104.

The backward inclined configuration of the centrifugal impeller 112 places the motor on the outside of the air stream with the centrifugal impeller 112 inside the housing 119, which is made possible by installing the variable speed motor and centrifugal impeller 112 at an angle. The variable speed motor and the centrifugal impeller 112 form an integrated drive unit assembly that can be removed from the housing 119 without removing the entire in-line draft inducer 110 from the stack system. While FIG. 3 shows the in-line draft inducer constructed with bolt flanges 115, the in-line draft inducer may alternatively include slip connection fittings.

FIGS. 4A and 4B further illustrate features of the heat recovery unit 106 and the bypass damper assembly 108 of the economizer 104 in FIG. 1. With reference to FIG. 4A, the heat recovery unit 106 is mounted on a guide rail assembly 302 within the economizer 104, where the guide rail assembly 302 is horizontally installed along a centerline of the economizer 104. The heat recovery unit 106 slides into the side of the housing 105 via the guide rail assembly 302 and a mounting flange secures the heat recovery unit 106 to the housing 105 to prevent leakage.

It should be emphasized that while the heat recovery unit 106 is shown horizontally mounted in the economizer 104, the heat recovery unit 106 may alternatively be vertically mounted in the economizer 104. The heat recovery unit 106 includes a top face 310 and a bottom face (not shown) formed by a series of copper tubing and fins. Referring briefly to FIG. 5, the heat recovery unit 106 also includes NPT (National Pipe Taper) water connectors 304 on a distal end of the heat recovery unit 106.

The heat recovery unit 106 comprises rectangular plate fins with a matrix of die-extruded tube collars. A sheet metal casing provides rigidity to the fin-tube assembly prior to tube expansion. After assembly, the tubes are expanded into the fin collars, which allows for a gap-free connection maximizing heat recovery unit performance and structural integrity. It should be appreciated that the design is extremely compact and efficient, and the pressure drop through the heat recovery unit may exceed 0.5 inWC.

Referring back to FIG. 4A, the bypass damper assembly 108 comprises a plurality of blades 308 a, 308 b, 308 c that are controlled by an actuator 301 configured to control a flow of gases through the economizer 104 by controlling the position of each blade 308 a, 308 b, 308 c. FIG. 4A illustrates the blades 308 a, 308 b, 308 c of the bypass damper assembly 108 in an open position to allow flue gases to pass through the lower chamber formed by the heat recovery unit 106 and the housing of the economizer 104 (when the heat recovery unit 106 is fully inserted into the economizer 104. FIG. 4B illustrates the heat recovery unit 106 inserted into the housing 105 of the economizer 104 and the blades 308 a, 308 b, 308 c of the bypass damper assembly 108 in a closed position to block the flow of flue gases through the lower chamber of the economizer 104.

Reference is made to FIG. 6, which is a side view of the economizer 104. As shown, the bypass damper assembly 108 further includes a series of lever arms 404 a, 404 b that are pivotally connected to the blades 308 a, 308 b, 308 c. The lever arms 404 a, 404 b are coupled together via a connecting member 402. By controlling the position of the lever arms 404 a, 404 b, the actuator 301 (FIG. 4A), is able to control the position of each blade 308 a, 308 b, 308 c and thus control the flow of flue gases through the chamber 410 formed by the heat recovery unit 106 and the housing of the economizer 104.

FIG. 7 shows another embodiment of the bypass damper assembly 108 in the economizer 104. For alternative embodiments, the bypass damper assembly 108 may comprise multiple round butterfly dampers, where the round damper blades are connected to a central shaft. For other embodiments, the bypass damper assembly 108 may comprise a single round damper where the actuator 301 (FIG. 4A) controls the position of the round damper such that the round damper is either in a neutral position or a blocking position, where the neutral position allows free flow of gases through the economizer 104, and where the blocking position inhibits the flow of gases. As shown in FIG. 7, the bypass damper assembly 108 may further comprise a fixed end plate 502 that is sealed. The fixed end plate 502 forces the flue gases to flow over the heat recovery unit when the damper assembly 108 is in a closed position.

FIG. 8 is a top view of the economizer 104 and further illustrates how the heat recovery unit 106 is slidably inserted into the economizer 104. FIG. 9 is a side view of the economizer 104 and further illustrates how the heat recovery unit 106 partitions the housing of the economizer 104 into an upper chamber 902 and a lower chamber 904. As described earlier in connection with FIGS. 2A and 2B, the bypass damper assembly 108 (FIG. 1) is controlled by a variable position actuator in the economizer 104, where the actuator configures the bypass damper assembly 108 to direct the exhaust flow in one of two exhaust flow configurations. In a first exhaust flow configuration, the flue gases flow pass over and through the heat recovery unit 106. Specifically, a turbulent exhaust flow is created such that flue gases flow through the lower chamber 904, through the heat recovery unit 106, and then into the upper chamber 902.

In a second exhaust flow configuration, the flue gases flow over and bypass the heat recovery unit 106. This configuration prevents over-heating of the coils in case the liquid inside the coils is not flowing or if the exhaust heat exceeds the performance of the heat recovery unit 106. The combination of the variable position actuator and the bypass damper assembly 108 allow modulation of the exhaust air flow over the heat recovery unit 106 so that a variable percentage of the exhaust air can pass through the heat recovery unit 106 and the remainder bypass the heat recovery unit 106.

Reference is made to FIG. 10, which is a flowchart illustrating an algorithm for controlling various components of the mechanical draft system 102 of FIG. 1 for facilitating the flow of flue gases according to various embodiments of the present disclosure. For various embodiments, the following algorithm is implemented in a mechanical draft system 102 with a damper assembly 108 (FIG. 1) on one end of the economizer 104 (FIG. 1) and a fixed end plate 502 (FIG. 7) at the other end of the economizer 104. Initially, when the mechanical draft system 102 is off, the damper assembly 108 will be in an open position, and the inline draft inducer 110 (FIG. 1) will be off. There will be no or at least very limited flow of fluid through the finned tubes in the heat recovery unit 106 (FIG. 1).

In block 1010, in response to a call for heat, the inline draft inducer 110 begins operation and speeds up until a predetermined draft set point in an external draft controller has been reached. For some embodiments, the draft set point is specified by the boiler manufacture. Specifically, the boiler manufacturer publishes a draft range for the specific boiler, which should be satisfied by the chimney/venting system. This set point is then used as the draft set point.

In block 1020, once the draft set point has been reached, the external draft controller releases the mechanical draft system 102 and allows the system to operate. In block 1030, an external valve opens, and fluid will begin to flow through the heat recovery unit 106. In block 1040, the actuator 301 will begin closing the damper assembly 108 so that the hot products of combustion will increasingly pass through the heat recovery unit 106. In block 1050, as the damper assembly 108 is closing and the products of combustion is channeled through the heat recovery unit 106, the inline draft inducer 110 will increase the fan speed in order to overcome the additional pressure loss created by the air flow through the heat recovery unit in order to maintain the predetermined draft point.

In block 1060, with the hot products of combustion flowing through the airside of the heat recovery unit 106, heat is transferred through the finned tubes of the heat recovery unit 106 and eventually to the fluids flowing inside the tubes. In block 1070, if the fluid temperature increases to a predetermined temperature (e.g., 200° F.), the actuator 301 gradually begins to open the damper assembly 108 to keep the temperature at or below the predetermined temperature by allowing flue gases to gradually bypass the heat recovery unit 106. Specifically, the damper assembly 108 will go from a fully closed position to a half open position and then to a fully open position.

In block 1080, if the fluid temperature reaches a second predetermined temperature (e.g., 210° F.), the actuator 301 completely opens the damper assembly 108 to allow the hot products of combustion to completely by-pass the heat recovery unit 106 (as shown in FIG. 2B) using “the path of least restriction” to prevent the fluids from starting to boil.

In block 1090, when the mechanical draft system 102 begins the process of turning off, the inline draft inducer 110 continues to operate in a post-purge mode and the damper assembly 108 will stay closed for a predetermined amount of time (e.g., 3 minutes), thereby allowing the products of combustion to be cleared from the heat recovery unit 106. In block 1100, after the post-purge period passes, the actuator 301 will completely open the damper assembly 108.

Reference is made to FIGS. 11 and 12, which illustrate different configurations in which the mechanical draft system 102 disclosed herein may be installed in a chimney system. In a first configuration, the economizer 104 and the in-line draft inducer 110 are coupled together via mating bolt flanges 115 (FIG. 1), where the mechanical draft system 102 is attached to a chimney in a substantially horizontal orientation, as shown in FIG. 11A.

In FIG. 11B, the economizer 104 and the in-line draft inducer 110 are coupled together via mating bolt flanges 115 (FIG. 1), where the mechanical draft system 102 is attached to a chimney in a substantially vertical orientation. FIG. 12 illustrates another configuration wherein the economizer 104 and the in-line draft inducer 110 are separated from each other in the chimney system. As shown, both the economizer 104 and the in-line draft inducer 110 include a tapered inlet and a tapered outlet to facilitate coupling to the ductwork.

It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. 

At least the following is claimed:
 1. A mechanical draft system, comprising: an in-line draft inducer comprising a motor and a backward-inclined impeller; and an economizer coupled to the in-line draft inducer, the economizer comprising a housing and a horizontally mounted heat recovery unit.
 2. The system of claim 1, wherein the motor is a variable speed motor and is mounted externally to a housing of the in-line draft inducer.
 3. The system of claim 1, wherein the economizer comprises at least one bypass damper controlled by an actuator, wherein the actuator is configured to control a position of the least one bypass damper to control a flow of gases through the economizer.
 4. The system of claim 3, wherein the at least one bypass damper comprises a fin having a semi-circular cross section.
 5. The system of claim 3, wherein the at least one bypass damper comprises one of a butterfly damper and a multi-blade damper.
 6. The system of claim 3, wherein the actuator is configured to configure the at least one bypass damper in one of a neutral position and a blocking position, wherein the neutral position allows free flow of gases through the economizer, and wherein the blocking position inhibits the flow of gases.
 7. The system of claim 1, wherein the heat recovery unit comprises a water-based radiator.
 8. The system of claim 1, wherein the heat recovery unit is mounted on a guide rail assembly within the economizer.
 9. The system of claim 1, wherein the guide rail assembly is horizontally disposed along a centerline of the economizer.
 10. The system of claim 1, wherein the economizer further comprises a tapered inlet for channeling exhaust flow.
 11. The system of claim 1, wherein the tapered inlet is coupled to a boiler unit and is configured to receive hot exhaust from the boiler.
 12. The system of claim 1, wherein the heat recovery unit comprises rectangular plate fins and a plurality of die-extruded tube collars.
 13. A mechanical draft system, comprising: an in-line draft inducer comprising a motor and a backward-inclined impeller; and an economizer detachably coupled to the in-line draft inducer, the economizer comprising a cylindrical housing for horizontally mounting a heat recovery unit that partitions the housing into an upper chamber and a lower chamber.
 14. The system of claim 13, wherein the economizer further comprises a dual-damper configuration controlled by separate actuators, wherein each actuator is configured to control a position of the corresponding damper to control exhaust flow through the economizer.
 15. The system of claim 14, wherein the actuator controls a position of each damper to allow flue gases entering the economizer to flow in one of two exhaust flow configurations, wherein the first exhaust flow configuration comprises exhaust flow through only one of the upper chamber and the lower chamber to bypass the heat recovery unit, and wherein the second exhaust flow configuration comprises turbulent exhaust flow through one of the lower chamber and upper chamber, through the heat recovery unit, and into the other chamber.
 16. The system of claim 14, wherein the actuator is configured to place each damper in one of a neutral position, a first blocking position, and a second blocking position; wherein the neutral position allows free exhaust flow, and wherein each of the first and second blocking positions inhibits exhaust flow.
 17. The system of claim 13, wherein the economizer further comprises: a single damper disposed on one end of the economizer; and a fixed end plate disposed on another end of the economizer; wherein the damper is controlled by an actuator, wherein the actuator is configured to control a position of the damper to control exhaust flow through the economizer.
 18. The system of claim 13, wherein the economizer comprises a circular inlet and a circular outlet, wherein the circular inlet and circular outlet each include mounting flange fittings.
 19. A method implemented in a draft controller in a mechanical draft system comprising an in-line draft inducer and an economizer, the economizer comprising a heat recovery unit and a damper assembly, the method comprising: in response to a heat recovery request, increasing a fan speed of the in-line draft inducer based on a predetermined draft set point value; upon reaching the draft set point value, opening a valve of the economizer to allow fluid to flow through the heat recovery unit; placing the damper assembly in a closed position to channel exhaust flow through the heat recovery unit; and in response to the damper assembly being placed in a closed position, increasing the fan speed of the in-line draft inducer to maintain the predetermined draft set point value.
 20. The method of claim 19, further comprising: in response to a temperature of the fluid flowing through the heat recovery unit reaching a first predetermined temperature, placing the damper assembly in a partially open position; and in response to a temperature of the fluid flowing through the heat recovery unit reaching a second predetermined temperature, placing the damper assembly in a fully open position. 